Further Investigations on Possible Correlations between QSOs and the Lick Catalogue of Galaxies

Abstract

We analyze the different contributing factors in a previous study by Seldner and Peebles (1979) who found statistically significant evidence for a correlation between a list of 382 QSOs at ÇbÇ > 40°, δ > -23° and the Lick counts of galaxies (m < 19.0), namely, that there are on the average 1.45 ±0.39 more galaxies within 15′ of a QSO than expected if QSOs were placed at random across the sky. Taking into account these different factors and using a larger sample of QSOs whose detection is not expected to bias our statistical results, we conclude that: i) There is no longer statistically significant evidence for an excess of Lick galaxies close to QSOs from our list considered as a whole. After removing the different possible biases, if there was any excess left in that previous study, it was rather due to radio QSOs and not to optical QSOs. This effect is marginal if we adopt a mean density of galaxies in a ring between 2° and 5°, and null if the mean density is taken between 1° and 2° from QSOs; ii) The whole correlation function w(θ) shows in general a hump between 1.°5 and 2°. This is either an off-set value or a maximum value preceding a slow decrease in w(6) between 1°.5 – 2° and 5°. This feature seems to pertain more to high redshift QSOs (z > 0.4) and to radio QSOs than to optical QSOs.